System for the visualization of exposure to ultraviolet radiation

ABSTRACT

Photochemical systems for the direct visualization of exposure to ultraviolet radiation that effect visible color changes involving a process in which a photoacid is formed upon irradiation of a nitro-substituted aromatic aldehyde with ultraviolet light and wherein proton transfer to a dye causes the dye to undergo a visible color change. The system undergoes such color change to an extent directly proportional to the cumulative amount of ultraviolet incident thereupon.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is a continuation-in-part of U.S. patentapplication Ser. No. 156,601, filed Mar. 1, 1988, now abandoned; whichin turn is a continuation-in-part of U.S. patent application Ser. No.027,640, filed Mar. 19, 1987, now abandoned.

BACKGROUND OF THE INVENTION

Ultraviolet light is that portion of the electromagnetic spectrumadjacent to the short wavelengths, or violet end, of the visible lightrange. The ultraviolet spectrum can be divided into two regions: thenear ultraviolet (near the visible spectrum), with wavelengths 200 to380 nm; and the far ultraviolet, with wavelengths 10 to 200 nm.Approximately ten percent of the energy from the sun is in theultraviolet range.

The near ultraviolet spectrum can also be divided into three subregions:ultraviolet A which has wavelengths that are generally in the range of320 to 380 nm; ultraviolet B which has wavelengths that are generally inthe range of 280 to 320 nm; and ultraviolet C which has wavelengths thatare generally in the range of 200 to 280 nm.

The solar ultraviolet intensity at the earth's surface depends upon avariety of factors including: the thickness of the ozone layer in theupper atmosphere, ozone absorbing ultraviolet radiation strongly between200 and 300 nm; the latitude; the elevation above sea level; theatmospheric turbidity; the time of day; the time of year; and localconditions such as clouds, fog, dust, and smoke.

Human exposure to ultraviolet radiation can produce effects ranging fromsuntan, to sunburn, to skin cancer. While there are protective devices,including clothing, oil, ointments, and lotions, which either absorb orreflect ultraviolet radiation or reduce its penetration, there are noportable, inexpensive, disposable, readily available, simple, devicesfor quantitatively detecting the extent of exposure to ultravioletradiation. Accordingly, it is desirable to have such a device which theconsumer can easily use to ascertain the total amount of ultravioletexposure.

Exposure to ultraviolet radiation can be measured either directly usingelectronic devices, such, as semiconductors, or indirectly using aspectrophotometer to quantitate the appearance or disappearance of achemical species reactive to ultraviolet radiation.

The photochemically mediated detection or measurement of exposure toradiation, especially in the visible and ultraviolet range, is known asactinometry. A classical liquid phase actinometer is described inHatchard et al., Proc. Royal. Soc., A235:518 (1956), based on thephotoreduction of ferrioxalate to form free ferrous ion which reactswith 1,10-phenanthroline causing a green to red color change.Frankenburger et al., U.S. Pat. No. 1,845,835, discloses an ultravioletsensitive solution, containing leucocyanides, carbinols, and sulfurouscompounds, which undergoes a direct, one-step, reversible color changeupon exposure to ultraviolet light. These systems will not specificallymeasure ultraviolet radiation as they are also sensitive to longerwavelengths.

Pavlickova et al., Col. Czechoslovak Chem. Comm., 51:36B (1986),describes a liquid phase actinometer, based on the photohydrolysisreaction of 3,4-dimethoxynitrobenzene, for the determination ofultraviolet light intensity. This liquid phase system does not haveoutput in the visible range and is intended for use with aspectrophotometric device. Thus, utility in "field" applications isseverely limited.

Reversible reactions have been suggested for use in actinometry. In thesolution systems of Burg, U.S. Pat. No. 3,561,969, for example, a lightsensitive solution undergoes a direct, one-step, reversible color changewith short exposures to white light. Actinometric complications andresultant inaccuracies are introduced by reversibility in such systems.

Solid state actinometers which rely on transformations of compoundsshowing no absorption in the visible range frequently have thedisadvantage of requiring use of a spectrophotometer. Examples of suchsystems are found in Bunce et al., J. Photochem., 23:219-231 (1983), andBunce et al., J. Photochem., 34:105-115 (1986), which disclose the useof azoxybenzene in blocks of polymethylmethacrylate. Some solid statesystems have the further disadvantage of requiring specially designedvacuum cells. For example, Cowell et al., J. Am. Chem. Soc., 90:1106(1968), discloses nitrobenzaldehyde in a film of polymethylmethacrylateas part of a system also requiring a spectrophotometer.

Disadvantages associated with some actinometric systems include theirvariable sensitivity and inability to discriminate among variouswavelengths of radiation--some systems being responsive to broad rangesof radiation and others limited to narrow ranges. Several patents (e.g.,Smith, U.S. Pat. No. 3,929,488; Harper et al., U.S. Pat. No. 4,296,194;and Shelnut et al., U.S. Pat. No. 4,348,47) disclose a process that isused in lithographic print plate manufacture and is responsive to amixture of both ultraviolet and visible light. Not only is the processnot specific for ultraviolet radiation, it does not have a dynamic rangeof responsiveness, is extremely reactive to low levels of radiation, andutilizes unstable diazonium compounds which are dangerous if they comein contact with the skin. In contrast, Schmidt et al., J. Photochem.,25:489-499 (1984), describes two systems specific for two distinctregions of ultraviolet light. One system, the photoxidation ofmeso-diphenyl- helinathrene, is recommended for the 475-610 nm range anda second system, including the photoreversible photocycle reversion ofthe endoperoxide of heterocoerdianthrone, is suited for re-usableactinometry in the 248-334 nm range. Again, systems such as these thatrequire a photometer are disadvantageous because their "output" cannotbe directly visualized. Further, the compounds employed are bothexpensive and potentially carcinogenic.

Another system responsive to both visible and ultraviolet radiationutilizes photoactivators or photosensitizers which enhance the densityof image formation upon exposure of leuco dyes to short periods ofultraviolet light without affecting the leuco dyes' reactivity tovisible light. See, e.g., Sprague et al., U.S. Pat. No. 3,121,632. Yetanother system responsive to both visible and ultraviolet radiation isdisclosed in Wainer, U.S. Pat. No. 3,112,200. Upon a several secondsexposure to light (250-400 nm), the halogen-containing compound of thedry photographic film is converted to a free radical, which leads to theproduction of significant amounts of acid and water, thereby resultingin a visible color change in the acid-base type indicator dispersedthroughout the film. Still another system responsive to both visible andultraviolet radiation is disclosed in Zweig, U.S. Pat. No. 3,903,423.Zweig discloses two systems; the first uses oxzolidine-diones whichdarken only in response to radiation shorter than 320 nm; the secondsystem uses photochromic cyclohexadiene compounds, such as xanthenones,which absorb not only from 320 nm and shorter, but also absorb atwavelengths longer than 320 nm, thereby requiring a filter to protectthe system from longer wavelength radiation, such as visible light.

Some measurement systems which do not require a photometer to determinethe amount of radiation exposure are simultaneously sensitive to bothfar ultraviolet radiation and to ionizing radiation and insensitive tonear ultraviolet radiation and therefore cannot be used for theselective measurement of exposure to near ultraviolet radiation. Forexample, McLaughlin, Intl. J. of Applied Radiation and Isotopes,17:85-96 (1966), discloses pre-activated colorless cyanides oftriphenylmethane dyes, which can be made into films which, uponirradiation with far ultraviolet or ionizing radiation change from acolorless to colored state. See also, McLaughlin et al., U.S. Pat. No.4,006,023. Similarly, Cerami et al., U.S. Pat. No. 4,466,941 discloses acomposition comprising a complex of leucocyanide and serum albuminwhich, upon exposure to x-rays, gamma rays, and/or other short wavelength radiation including, ultraviolet radiation, results in theappearance of color.

Systems for detecting ionizing radiation wherein exposure to ionizingradiation causes a halogen-containing compound to form a halo-acid whichin turn causes an acid-sensitive dye to change color are disclosed innumerous patents. See, e.g., Vale et al., U.S. Pat. No. 3,290,499;Huebner et al., U.S. Pat. No. 3,691,380; Matsumoto et al., U.S. Pat. No.3,743,846; Hori et al., U.S. Pat. No. 3,899,677; and Lemahieu et al.,U.S. Pat. No. 4,008,085. In general, these systems are either heatsensitive or visible light sensitive. To the extent that they displayultraviolet light sensitivity, none are noted to be specific forultraviolet light detection. None of these systems is suitable for usein applications requiring low toxicity.

Reversible photochromic materials useful in the preparation ofphotochromic plastic films, sheets, and opthalmic lenses and rapidlyresponsive to exposure to light are disclosed in Uhlmann et al., U.S.Pat. No. 4,012,232 and Wagner et al., U.S. Pat. No. 3,666,352.Generally, these materials change their transmission or reflectance uponbeing subjected to ultraviolet or visible irradiation and subsequentlyrevert to their original state upon exposure to a different wavelengthof radiation, or removal of the initial light source. Photochromicpolymers capable of undergoing reversible changes between two chemicalspecies induced by light absorption can be used for reversible opticalinformation storage and have been suggested for actinometric uses inbadges to detect unsafe levels of ultraviolet exposure. Wilson, Phys.Technol., 15:233 (1984). However, such a suggestion does not take intoaccount the reversibility of the reaction nor the responsiveness of thereaction to visible light and resultant erroneous readings obtained whenattempting to ascertain the extent of ultraviolet exposure.

Chem. Eng. & News, 64:77 (September 1986), reports that a system forindication of the passage of time and exposure to elevated temperaturesis being developed as a spoilage indicator for perishable products. Theindicators consist of filter paper dipped in a solution containing aleuco base dye and orthonitrobenzaldehyde. Commencing with a discretephotoactivation step, an oxidation process causes the indicator to beginto undergo a progressive color change in the acidified environment whichis both time and temperature dependent. The rate at which the colorchange appears can be adjusted in accordance with the shelf-life of anygiven product so that a color change appears more quickly for some goodshaving a short shelf-life. Visible light above 400 nm does not activatethe system. After initial photoactivation, the dyestuff color changereaction of this system is responsive to the passage of time andincreased temperature; however, the system cannot measure the extent ofsubsequent exposure to ultraviolet radiation.

In sum, numerous actinometric devices and systems have been proposed inthe prior art. None has been totally responsive to the need in the artfor systems allowing ready visualization of cumulative exposure toultraviolet light which are easily constituted from relativelyinexpensive and non-toxic components and which display specificity forultraviolet light and relative insensitivity to heat and the passage oftime.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a film that is substantially oxygenimpermeable and changes color in response to exposure to ultraviolet(UV) radiation. The film comprises a mixture of a hydrophilic polymer, anitro-substituted aromatic aldehyde for producing hydrogen ions inresponse to UV radiation and at least one dye that is substantiallyinsensitive to changes in temperature and sensitive to changes inhydrogen ion concentration.

The films of the present invention can optionally contain water.

Another embodiment of the present invention is directed to anultraviolet radiation dosimeter that comprises an ultraviolet radiationtransparent moisture barrier adhered to and surrounding the films of thepresent invention.

The ultraviolet radiation dosimeter of the present invention canoptionally contain an ultraviolet-A radiation filter that covers atleast a portion of the surface of the film that is to be exposed toultraviolet radiation.

The ultraviolet radiation dosimeter of the present invention can alsooptionally contain a color standard chart in close visual proximity tothe film. The dosimeter can also contain means to affix the dosimeter toa user such as an adhesive layer of velcro strip or the like.

The color change is proportional to the cumulative amount of exposure toultraviolet radiation and one or more dyes can be used to provide singleor multiple color changes in response to changes in hydrogen ionconcentration caused by cumulative exposure to ultraviolet radiation.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The films of the present invention comprise a mixture of a hydrophilicpolymer, a photoacid progenitor compound such as a nitro-substitutedaromatic aldehyde for producing an acid in response to UV radiation andat least one dye that is substantially insensitive to changes intemperature and sensitive to changes in hydrogen ion concentration.

The films of the present invention are substantially oxygen impermeable,temperature stable, hydrophilic and have high tensile strength. Thus,films of the present invention provide good barriers against oxygen, donot soften or become brittle upon exposure to high or low temperatures,remain non-tacky at high humidity and are abrasion and tear resistant.The films of the present invention do not change color in response totemperature changes or exposure to the atmosphere (oxygen) but changecolor in response to cumulative exposure to ultraviolet radiation.

As used herein, the term "substantially oxygen impermeable" is intendedto mean that less than about 1×10⁻¹² cubic centimeter of oxygen persecond is passed through a 1 square centimeter area of film when thepressure across a film thickness of 1 centimeter is 1 centimeter ofmercury and the temperature is 25° C.

As used herein the term "hydrophilic" is intended to mean that the filmabsorbs water at a rate of more than 0.5 percent by weight in atwenty-four hour period.

Hydrophilic polymers are used to prepare the films of the presentinvention. Representative hydrophilic polymers include polyvinylalcohol, derivatized cellulose and polyethylene glycol and the like.

The term "nitro-substituted aromatic aldehydes" is intended to includeany aromatic aldehyde that contains a nitro substituent. Preferredaldehydes are those wherein the nitro substituent is in an orthoposition with respect to the aldehyde group. Representative aldehydesinclude ortho-nitrobenzaldehyde; 2,4-dinitrobenzaldehyde;2,6-dinitrobenzaldehyde; and orthonitrocinnamaldehyde.Ortho-nitrobenzaldehyde is the most preferred aldehyde for use in thepresent invention, particularly the bisulfite adduct thereof.

Surfactants can also be used in the films of the present invention toimpart wetability and leveling in manufacture. Representativesurfactants which can be utilized are sodium lauryl sulfate, sodiumdodecylbenzene sulfonate, nonylphenol derivatives and the like.

The films of the present invention preferably contain water in an amountsufficient to permit the transfer of protons from the photoacid to thedyestuff. Preferred films of the present invention comprise a mixtureof:

from about 50 to about 99 weight percent polyvinyl alcohol;

from about 0.5 to about 50 weight percent water;

from about 0.01 to about 5 weight percent of at least one acid-sensitivedye that is substantially insensitive to changes in temperature;

from about 0.05 to about 5 weight percent of a surfactant; and

from about 1 to about 40 weight percent nitro-substituted aromaticaldehyde.

The films of the present invention are useful as an exposure indicatorin a UV radiation dosimeter. Thus, a UV dosimeter of the presentinvention comprises a film of the present invention surrounded by a UVradiation transparent moisture barrier. Typically, such a moisturebarrier is a film of polyethylene, polymethylacrylate and the like.

Preferably, a UV dosimeter of the present invention further includes aUV-A radiation filter that covers at least a portion of the surface ofthe UV exposure-indicating film. Particularly preferred are filtersoperating to preferentially exclude UV radiation of wavelengths greaterthan about 320 nanometers.

Preferably, a UV dosimeter of the present invention includes a colorstandard chart affixed to the dosimeter in close visual proximity to theexposure-indicating film. The chart contains discrete areas of colorcorresponding to the colors displayed by the indicting film in responseto preselected amounts of UV radiation.

A wide variety of dyes is suitable for use in systems (films anddosimeters) of the present invention. They may be initially colored orcolorless; soluble in organic or aqueous solutions; and subject to oneor more color changes over a range of pH values. Dyes sensitive tochanges in pH may be used singly, or in combination with each other, orin combination with dyes relatively insensitive to changes in pH, toproduce a broad range of color changes ("phototranschromic" effects).Some of the films of the invention comprise a mixture of two or moredyestuffs, each dyestuff having an initial color state (which may bedifferent from or the same as the other dyestuff's initial color state),a final color state (which may be different from or the same as theother dyestuff's final color state) and, in addition having intermediatecolor state(s) that are not additive mixtures of the initial and finalcolor states of the particular system selected.

A preferred dye system of the present invention is selected to provide acolor change upon initial exposure to ultraviolet radiation and furthercolor changes upon low, medium and maximum levels of exposure.Particularly preferred are systems where bromophenol blue and m-cresolpurple are present in about equal molar amounts.

Representative dyes that can be utilized in the present inventioninclude aniline blue, methyl violet, crystal violet, ethyl violet,brilliant green, oralochite green oxalate, methyl green, cresol red,quinaldine red, para methyl red, metanil yellow, thymol blue, m-cresolpurple, orange IV, phenylazoaniline, erythrosin B, benzopurpurin 4B,bromophenol blue, congo red, methyl orange, ethyl orange, bromocresolgreen, resazurin, ethyl red, methyl red, alizarin red, bromocresolpurple, chlorophenol red.

In certain embodiments of the invention, the film includes a solubilizerfor the nitro-substituted aromatic aldehyde (e.g., an adduct formingagent such as sodium meta bisulfite), a pH adjuster (such as sodiumhydroxide), an anti-oxidant (such as hexamethylenetetramine) and/or anorganic or aqueous buffering agent. Suitable buffering agents, such asTris-HCl, sodium deoxycholate, and sodium phosphate, can be used tolessen or to increase the responsiveness of the films. The relativeproportions of nitro-substituted aromatic aldehyde, dyes, medium,solubilizer, anti-oxidant, pH adjuster, and buffer are subject to widevariations depending upon the particular use contemplated and theparticular color changes desired.

The following examples illustrate the production of materials whichundergo visible color changes upon exposure to near ultraviolet light.Also illustrated are materials which can be constructed to undergo thiscolor change to an extent directly proportional to the cumulative amountof ultraviolet light incident upon the materials and which can bevariously constructed to differ in terms of initial, intermediate, andfinal color states and in terms of the total amount of ultravioletexposure required for a visible color change to occur. Also illustratedare exemplary systems allowing for the convenient measurement of theextent of ultraviolet illumination reaching a particular location,object, or person which can be readily used as a means for monitoringpersonal exposure to ultraviolet light from various sources, includingthe sun. Various other uses are anticipated.

More specifically, Examples 1-5 illustrate the preparation of plasticfilms and other thin layers or solid objects which exhibitphototranschromic effects. Examples 6-10 illustrate the use of multiplenitro-substituted aromatic aldehydes. Example 11 demonstrates the verybroad range of dyes which can be effectively utilized. Example 12illustrates the use of a solubilizer. Examples 13-20 illustrate the useof buffers and pH adjusters to modify aspects of the dyestuff colorchange reaction. Examples 21-27 relate to additional specific examplesillustrating procedures for making phototranschromic films, inks, toys,and imaging materials. Example 28 relates to the preparation and use ofcrystalline ortho-nitrobenzaldehyde bisulfite adduct; Example 29 relatesto the preparation of multilaminate films; Example 31 relates to thepreparation of very thin films: Example 32 relates to the use of ananti-oxidant; Examples 33 and 34 relate to the preparation of films frommultiple dyes where the films display intermediate colors that are notsimple mixtures of the initial and final color states of the films andto the use of ultraviolet absorbing inks in combination therewith; andExample 35 relates the conversion of a black, white, and multiple shadesof grey image into a colored image having enhanced contrast and detail.The examples which follow are for illustrative purposes and are notintended in any way to limit the scope of the Applicant's invention.

Other aspects and advantages of the present invention will be apparentupon consideration of the following representative examples.

EXAMPLE 1

Solutions for use in making films and other thin layers according to theinvention, containing ortho-nitrobenzaldehyde and polyvinyl alcohol, areprepared as follows. Seven hundred mg of polyvinyl alcohol (molecularweight, ca. 86,000, Aldrich Chemical Co., Milwaukee, Wis.) is dissolvedin 10 ml of boiling water and 15.5 mg (10 mM) ortho- nitrobenzaldehydeis added to the still hot solution. The solution is made 1 mM withrespect to any one of the dyes set out in Table 1, below. The pH of thesolution is adjusted until the dye is in its basic form by addition of 1M sodium hydroxide in the volumes indicated.

                  TABLE 1                                                         ______________________________________                                                          microliters                                                 Indicator Dye     1 M NaOH                                                    ______________________________________                                        1.      bromothymol blue                                                                            60                                                      2.      ethyl red     40                                                      3.      m-cresol      60                                                      4.      neutral red   60                                                      5.      chlorophenol red                                                                            30                                                      6.      bromocresol green                                                                            0                                                      7.      methyl red    30                                                      8.      bromophenol red                                                                             20                                                      9.      hematoxylin   60                                                      10.     alizarin      30                                                      11.     propyl red    30                                                      12.     bromophenol blue                                                                             0                                                      ______________________________________                                    

In Example 2, a solution of an ultraviolet reactive compound, such asorthonitrobenzaldehyde, an acid-sensitive dye as set out in Table 1, anda medium, such as polyvinyl alcohol, is applied to a flat surface andallowed to evaporate, leaving a thin plastic film. Such a film isinitially either blue or green, depending upon the pH adjustment of theinitial solution. Upon exposure to near ultraviolet light, theorthonitrobenzaldehyde is converted to orthonitrosobenzoic acid, theacid stoichiometrically converts the dye, e.g., from its basic to itsacid form, and the color of the film changes. Bromothymol blue, forexample, changes from blue to green-yellow to yellow depending upon thelength of exposure.

EXAMPLE 2

This example demonstrates the color changes observed for twelvedifferent films all having different indicator dyes upon exposure to 0,15, or 60 minutes of solar illumination.

Three 25 μL aliquots of any one of the solutions described in Example 1are pipetted onto a glass plate and allowed to air dry for approximatelyone hour. The dried films are subjected to 0, 15 or 60 minutes of solarillumination on a clear February day in San Diego, Calif. and the colorsnoted. The observed color changes are listed in Table 2.

                  TABLE 2                                                         ______________________________________                                                     OBSERVED COLOR                                                                  Initial  15 min.   60 min.                                     INDICATOR DYE  Color    Sunlight  Sunlight                                    ______________________________________                                        1.     bromothymol blue     green-  yellow                                           blue                 yellow                                            2.     ethyl red   yellow   red-    red                                                                   yellow                                            3.     m-cresol    lilac    yellow  yellow                                           purple                                                                 4.     neutral red orange   orange  orange                                    5.     chlorophenol                                                                              purple   yellow- yellow-                                          red                  purple  purple                                    6.     bromocresol blue     light   green-                                           green                blue    blue                                      7.     methyl red  yellow   yellow- red                                                                   red                                               8.     bromophenol purple   purple- purple-                                          red                  yellow  yellow                                    9.     hematoxylin red      orange  light-                                                                        orange                                    10.    alizarin    light    v. light                                                                              white                                                        purple   purple                                            11.    propyl red  yellow   red-    red-                                                                  yellow  orange                                    12.    bromophenol blue     blue    blue                                             blue                                                                   ______________________________________                                    

The following example, Example 3, relates to the use of ultravioletsensitive solutions which can be applied to surfaces such as cloth,paper, cardboard, plastics, wood, metals, and the like.

EXAMPLE 3

To 10 ml of acetone 10% in polyvinyl acetate, (medium molecular weight,Aldrich Chemical Co., Milwaukee, Wis.) and 100 mM inorthonitrobenzaldehyde was added 300 μL of a 100 mM suspension ofbromothymol blue in ethanol giving a final 3 mM dye concentration. 200μL of 1 M NaOH in water was added with thorough shaking. This solutionwas loaded into a paint sprayer of the air brush type and applied to acardboard surface which had been previously washed with ammoniumhydroxide and air dried. Thus applied, the solution formed a blue,slightly tacky, layer which rapidly dried to the touch. When placed indirect sunlight for 30 minutes, the color changed from blue throughgreen to yellow.

The films and coatings prepared rising polyvinyl acetate were notcolorfast and lost the ability to respond to UV radiation over usefulstorage periods (3 to 60 days).

The following example, Example 4, demonstrates that an appropriate solidsupport can be employed onto which a buffer may be applied in a complexpattern.

EXAMPLE 4

A 20×20 cm plastic-backed diethylaminoethyl cellulose (DEAE) thin layerchromatography sheet (Baker-flex, J. T. Baker Chemical Co.;Phillipsburg, N.J.) was placed in an ink jet printer such as a Canon PJ1080A and imprinted with a pattern using a 100 mM solution of sodiumdeoxycholate in water rather than using ink. The printed sheet was thencoated with a solution of 2-ethoxy-ethoxy-ethanol, 1 mM in bromothymolblue in its basic form and 10 mM in orthonitrobenzaldehyde by sprayingwith an air brush. In some cases Saran™ membrane was laid over the stillmoist film. On exposure to ultraviolet light the image of the depositedbuffer could be discerned by its retardant effect on the acidificationof the indicator dye. However, when the Saran™ membrane was not present,the system was not colorfast and lost its ability, over time, to respondto UV radiation.

Various moldable plastics can also be used as the support medium asdemonstrated in Example 5.

EXAMPLE 5

To 10 ml of Petrarch SS curable silicone dispersion (Petrarch Systems,Inc., Bristol, Pa.) was added 100 mg orthonitrobenzaldehyde (66 mM) and100 μL of a 100 mM solution of erythrosin B. The dispersion was vortexedthoroughly and 4 ml was applied to a clean glass plate and allowed todry for eight hours. The remainder was left in a 20 ml vial, where in itcongealed into a soft, pliable, dry, but slightly sticky pellet. Thepellet and the film from the glass plate were placed under ultravioletillumination for twenty minutes in which time the exposed film turnedfrom charry red to a light pink and the exposed surface, but not theinterior, of the pellet did likewise. However, colorfastness was lostover time.

The following example, Example 6, compares the in situ reactivity of2,4-dinitrobenzaldehyde to that of orthonitrobenzaldehyde in the samemedium and with the same dye and demonstrates that the former aldehydeis also an effective proton progenitor compound for use in systems ofthe invention.

EXAMPLE 6

To 20 ml of a 10% solution of polyvinylacetate (medium molecular weight,Aldrich Chemical Co., Milwaukee, Wisconsin) in ethoxyethoxyethanol, wasadded 196 mg of 2,4-dinitrobenzaldehyde (50 mM) and, with considerableagitation to effect complete dissolution, 200 μL of a 100 mM aqueoussolution of erythrosin B and 100 μL of a 1 M solution of sodiumhydroxide.

A second solution was prepared similarly except for the substitution of151 mg of orthonitro-benzaldehyde for the 2,4-dinitrobenzaldehyde. Bothsolutions were poured onto clean glass plates and allowed to evaporatefor 24 hours at room temperature. Representative strips from each filmwere placed in direct noontime sunlight for two hours. The filmcontaining the 2,4-dinitrobenzaldehyde turned from an intense,fluorescent fuchsia to a quiescent golden yellow. The film containingthe ortho- nitrobenzaldehyde turned a reddish-orange indicative of onlypartial acidification of the dye.

The following two examples, Example 7 and Example 8, demonstrate the useof 2,4-dinitrobenzaldehyde with two different dyes, erythrosin B andpropyl orange.

EXAMPLE 7

An acetone solution, 10% in polyvinylacetate, (medium molecular weight,Aldrich Chemical Co., Milwaukee, Wis.), 100 mM in2,4-dinitrobenzaldehyde, and 1 mM in erythrosin B was poured onto aclean glass plate and allowed to evaporate into a thin film. When placedin direct sunlight for 45 minutes the film turned from a light fuchsiato a tangerine pink.

EXAMPLE 8

A similar film, made as in the preceding example, Example 7, but with 3mM propyl orange and 5 mM NaOH, turned from an intense orange to anintense orange-red.

The following examples, Example 9 and Example 10, demonstrate that theamount of acid generated upon exposure to ultraviolet light isproportional to the exposure time and also depends upon the amount ofphotoacid progenitor substrate remaining as the reaction progresses.

EXAMPLE 9

Acidity generated by ultraviolet exposure of a polyvinyl alcohol filmcontaining the orthonitrobenzaldehyde (ONB) bisulfite adduct (preparedaccording to Example 12, described below) is quantitated by titrationwith 10 mM NaOH. Solutions I-IV, made from aqueous solutions in thevolume proportions listed in Table 3, are applied to clean glass plateswhere they are allowed to evaporate, depositing thin clear films on theplates.

                  TABLE 3                                                         ______________________________________                                                        SOLUTIONS                                                     COMPONENT         I     II       III IV                                       ______________________________________                                        500 mM ONB        5     10       5   5                                        sodium bisulfite complex                                                      8% polyvinyl alcohol                                                                            40    40       40  40                                       100 mM bromothymol blue                                                                         0     0        0.5 0                                        100 mM propyl red 0     0        0   1.5                                      water             5     0        4.5 3.5                                      1 M NaOH          0.5   0.5      0.5 0.5                                      ______________________________________                                    

After 8 hours drying, squares 1"×1" are cut from the films and weighed.These are exposed to a Fotodyne, (New Berlin, Wis.) ultraviolettransilluminator for periods of 0 to 240 minutes after which they aredissolved in 4 ml of water and titrated with 10 mM NaOH to the pHobserved for the time zero control. In the tables below, Tables 4, 5, 6,and 7, initial pH is the pH of the exposed, dissolved, square prior totitration.

                  TABLE 4                                                         ______________________________________                                        Solution I; titrated to control pH 7.80                                       (50 mM ONB and no dye)                                                        Time    Weight      Initial Micromoles/gram                                   (min)   (mg)        pH      required                                          ______________________________________                                        10      38.6        5.31     88                                               20      36.7        4.60    155                                               40      34.7        3.97    202                                               80      34.8        3.82    287                                               160     35.7        3.65    328                                               240     33.2        3.63    340                                               ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Solution II; titrated to control pH 7.09                                      (100 mM ONB and no dye)                                                       Time    Weight      Initial Micromoles/gram                                   (min)   (mg)        pH      required                                          ______________________________________                                        10      57.4        4.84     96                                               20      55.6        4.43    140                                               40      58.0        4.32    157                                               80      55.2        4.06    199                                               160     57.5        3.88    231                                               240     51.8        3.76    290                                               ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        Solution III; titrated to control pH 7.65                                     (50 mM ONB and 1 mM bromothymol blue)                                         Time    Weight      Initial Micromoles/gram                                   (min)   (mg)        pH      required                                          ______________________________________                                        10      37.7        5.32     98                                               20      36.3        4.88    151                                               40      39.1        4.69    169                                               80      38.3        4.44    204                                               160     34.8        4.17    276                                               240     33.2        4.06    292                                               ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        Solution IV; titrated to control pH 7.43                                      (50 mM ONB and 3 mM propyl red)                                               Time    Weight      Initial Micromoles/gram                                   (min)   (mg)        pH      required                                          ______________________________________                                        10      33.7        5.97     77                                               20      36.5        5.24     93                                               40      38.3        4.86    128                                               80      36.7        4.63    153                                               160     36.3        4.42    212                                               240     37.8        4.26    193                                               ______________________________________                                    

EXAMPLE 10

A repetition of the preceding example, Example 9, was performedsubstituting 2,4-dinitrobenzaldehyde for ortho-nitrobenzaldehyde.However, due to the lower solubility of the 2,4-dinitrobenzaldehydebisulfite adduct, it was not possible to prepare a 500 mM stocksolution. Thus, 1.4 ml lM sodium bisulfite was added to 24 ml 8%polyvinyl alcohol, and to this solution was added, with heating, 250 mg2,4-dinitrobenzaldehyde. The solution, 50 mM in 2,4-dinitrobenzaldehyde,was poured onto a clean glass plate and evaporated during which timesome of the aldehyde crystallized in the film. Squares cut from thisfilm were treated as those in Example 9 and were titrated to a controlpH of 5.18. The following results were obtained.

                  TABLE 8                                                         ______________________________________                                        Time    Weight      Initial Micromoles/gram                                   (min)   (mg)        pH      required                                          ______________________________________                                        10      57.9        4.58    20                                                20      48.5        4.25    33                                                40      52.1        4.00    46                                                80      57.8        3.61    66                                                160     51.7        3.49    77                                                240     56.9        3.33    98                                                ______________________________________                                    

A very broad range of dyes can be effectively utilized as illustrated inExample 11.

EXAMPLE 11

The pH sensitive dyes in the following table were dissolved to aconcentration of 1 mM (unless otherwise noted) in solutions which were50 mM in ortho-nitrobenzaldehyde-bisulfite adduct (prepared according toExample 12, described below), and 7.2% in polyvinyl alcohol. One molarsodium hydroxide was added to the solutions until the dyes were in theirbasic form. The several solutions were poured onto clean glass platesand allowed to evaporate overnight. They were exposed to direct noontimesunlight for various periods of time (indicated in minutes) and theirranges of colors recorded as indicated in Table 9.

                                      TABLE 9                                     __________________________________________________________________________    OBSERVED COLOR                                                                (time in minutes)                                                             DYE               INITIAL/INTERMEDIATE/FINAL                                  __________________________________________________________________________    Alizarin, (3 mM)  violet(0)/dusty rose(5)/gold(30-180)                        Alizarin yellow R light yellow(0)/medium gold(30)/dark gold (90-180)          Alizarin red s    dusty pink(0)/orange-tan(30-180)                            Benzopurpurin 4B  red(0 to 180)                                               4,4'-bis(4-amino-1-naphthyl-azo)-                                                               violet(0)/red-brown(30-180)                                 2,2'-stilbene-disulfonic acid                                                 Brasiline         turquoise(0)/lavender (5)/dusty rose(10)/orange-tan(30-1                      80)                                                         Bromocresol green royal green(0)/dark green(5-180)                            Bromocresol purple                                                                              purple(0)/dark brown(5)/dark olive(30)/light                                  olive(90-180)                                               Bromophenol blue  purple(0)/dark green-green(5-180)                           Bromophenol red   red-brown(0)/golden brown(5)/brown(30-180)                  Bromothymol blue  royal blue(0)/dark green(5)/gold(45-180)                    Bromoxylenol, (3 mM)                                                                            dark blue(0)/dark green(5-180)                              Carminic acid     pink-violet(0)/light pink(5)/coral(30-180)                  Chlorophenol red  burgundy(0)/golden brown(5)/yellow(15-180)                  Congo red         salmon(0)/subtle change to dark salmon at 180               o-Cresolphthalein initial color is unstable even in absence of                                  illumination                                                m-Cresol purple   navy blue(0)/yellow(5)/gold(30-180)                         Cresol red        burgundy(0)/golden brown(5)/gold(15-180)                    Curcumin          reddish brown(0)/light yellow(5)/gold(30-180)               3-(4-Dimethylamino-1-naphthyl-azo)-                                                             light yellow(0)/light tan(90-180)                           4-methoxybenzene-sulfonic acid                                                4-(4-Dimethylaminophenylazo benzoic                                                             dye precipitates from solution                              acid                                                                          Direct red        electric magenta(0)/scarlet to scarlet-red(30-180)          Eriochrome black T                                                                              turquoise(0)/dark tan(15-180)                               Erythrosin B, (2 mM)                                                                            burnt pink(0)/dark pink(5)/orange(30-180)                   4-(4-Ethoxyphenylazo)-3-phenylene-                                                              yellow(0)/light gold(5)/dark gold(15-180)                   diamine hydrochloride                                                         Ethyl orange      gold(0)/dark gold(5)/orange(30-180)                         Ethyl red         yellow(0)/light pink(5)/medium pink to reddish                                pink(10-180)                                                Ethyl violet      medium blue(0)/blue-grey(90-180)                            Hematoxylin       beige(0)/light beige(5)/yellow-tan(30-180)                  Lacmoid           grayish-turquoise(0)/dark brown(30-180)                     Litmus            cornflower blue(0)/lavender(5)/orange-tan(30-180)           Metanil yellow    yellow(0)/gold(90-180)                                      Methyl green      aqua blue(0)/aqua green(90-180)                             Methyl red, (6 mM)                                                                              yellow(0)/orange(5)/red(10)/scarlet(30-180)                 Naphtholphthalein bismuth grey(0)/clear(5)/yellow-tan(30-180)                 Naphthyl red hydrochloride                                                                      dye precipitates from solution                              Neutral red, (3 mM)                                                                             orange-tan(0)/light red(5)/dark orange-tan(30-180)          Nile blue A       sky blue(0)/light green(10)/swamp green(30-180)             2-Nitrophenol     dye degrades under ultraviolet illumination                 3-Nitrophenol     dye degrades under ultraviolet illumination                 4-Nitrophenol     dye degrades under ultraviolet illumination                 Orange I          red(0)/orange(5-180)                                        4-(Phenylazo)diphenylamine                                                                      light yellow(0)/light beige(90-180)                         Phenol red        scarlet-red(0)/red(5)/gold(10-180)                          Propyl red, (3 mM)                                                                              gold(0)/red(5)/scarlet-red(30-180)                          Resazurin, (2 mM) dark purple(0)/dk. brown-red(5)/red(30)/dark                                  orange(45-180)                                              Thiazole yellow G yellow(0-180)                                               Thymol blue       light olive(0)/light gold(5)/dark gold(30-180)              Thymolphthaleine  initial color is unstable in absence of illumination        Tropaeoline OO    gold(0)/medium gold(30)/dark gold(90-180)                   p-Xylenol blue    dark olive(0)/gold(5-180)                                   __________________________________________________________________________

Films fabricated with a hydrophilic polymer as polyvinyl alcoholexhibited incompatibility of the ortho-nitrobenzaldehyde (ONB) compoundwhen utilized in levels about 10 mM. In order to use ONB in aqueoussolutions at higher levels and to prevent crystallization or powderingwhen formed into a film, it is necessary to convert the aldehydes into awater soluble adduct: This was accomplished by preparing an ONBbisulfite adduct, thereby allowing the use of much higher concentrationsof ONB in the film. The presence of relatively high amounts (≧ 25 mM) ofONB in the film results in a film that responds more rapidly to UVradiation.

Example 12 illustrates the preparation of aldehyde bisulfite adducts.Examples 13-16 relate to procedures wherein a necessarily highconcentration of ortho-nitrobenzaldehyde bisulfite adduct is utilizedwhich is higher than the concentration obtainable without a solubilizingagent such as bisulfite. Examples 15-16 contain, in addition, thebuffer, Tris-HCl.

EXAMPLE 12

The preparation of aldehyde bisulfite adducts is accomplished asfollows. To 400 ml of a solution containing 20.9 grams sodiummetabisulfite (550 mM) in water is added 30.2 gramsorthonitrobenzaldehyde. The solution is stirred and brought to 60° C.The aldehyde dissolves slowly, and remains in solution after thetemperature is lowered. In contrast, addition of the bisulfite to aheated suspension of the aldehyde in water does not result in a clearsolution, nor does adding both aldehyde and bisulfite to heated water.

Similar procedures, applied to 2,4-dinitrobenzaldehyde,3,5-dinitrobenzaldehyde, and 0-nitrocinnamaldehyde, were effective insolubilizing these aldehydes up to a concentration of 50 mM.

EXAMPLE 13

Solutions were prepared as in Example 1 except that theortho-nitrobenzaldehyde was added as a solution of its bisulfite adductin a 10% excess of sodium bisulfite. The concentration ofortho-nitrobenzaldehyde bisulfite adduct in the final solutions was 25mM. All other concentrations were similar to those in Example 1. The pHof the solutions was adjusted as indicated in Table 10.

                  TABLE 10                                                        ______________________________________                                                          microliters                                                 INDICATOR DYE     1 M NaOH                                                    ______________________________________                                        1.      bromothymol blue                                                                            40                                                      2.      ethyl red     30                                                      3.      m-cresol purple                                                                             50                                                      4.      neutral red   50                                                      5.      chlorophenol red                                                                            40                                                      6.      bromocresol green                                                                            0                                                      7.      methyl red    20                                                      8.      bromophenol red                                                                             40                                                      9.      hematoxylin   100                                                     10.     alizarin      60                                                      11.     propyl red    20                                                      12.     bromophenol blue                                                                             0                                                      ______________________________________                                    

EXAMPLE 14

Three 25 μL aliquots of the solutions of Example 13 are pipetted onto aglass plate and allowed to air dry for approximately 1 hour. The driedfilms are subjected to 0, 15 or 60 minutes of solar illumination on aclear February day in San Diego, Calif. and the colors noted. Theobserved color changes are listed in Table 11.

                  TABLE 11                                                        ______________________________________                                                     OBSERVED COLOR                                                                  Initial  15 min.   60 min.                                     INDICATOR DYE  Color    Sunlight  Sunlight                                    ______________________________________                                        1.     bromothymol green    green-  yellow                                           blue                         yellow                                    2.     ethyl red   yellow   red-    red                                                                   yellow                                            3.     m-cresol    lilac    yellow  yellow                                           purple                                                                 4.     neutral red orange   orange  orange                                    5.     chlorophenol                                                                              purple   yellow- yellow                                           red                  purple                                            6.     bromocresol blue     lt. blue                                                                              green-                                           green                        yellow                                    7.     methyl red  yellow   yellow- red                                                                   red                                               8.     bromophenol purple   purple- yellow                                           red                  yellow                                            9.     hematoxylin red      orange  light                                                                         yellow                                    10.    alizarin    light    v. light                                                                              light                                                        purple   purple  yellow                                    11.    propyl red  yellow   red-    yellow-                                                               yellow  pink                                      12.    bromophenol blue     blue    green-                                           blue                         yellow                                    ______________________________________                                    

EXAMPLE 15

To one-ml aliquots of the solutions of Example 13 is added 6 μL of 1 MTris-HCl at pH 8.0. This is equivalent to 3 mM titratable Tris base inthe final solutions. Three 25 μL aliquots of the resulting solutions arepipetted onto a glass plate and allowed to air dry. The drying iscomplete in one hour. The dried films are subjected to 0, 15, or 60minutes of solar illumination on a clear February day in San Diego,California and the colors noted. The observed color changes are listedin Table 12.

                  TABLE 12                                                        ______________________________________                                                      OBSERVED COLOR                                                  INDICATOR DYE   Initial  15 min.   60 min.                                    WITH 3 mM Tris-HCl                                                                            Color    Sunlight  Sunlight                                   ______________________________________                                        1.     bromothymol  blue-    green   yellow                                          blue         green                                                     2.     ethyl red    yellow   yellow- red                                                                   red                                              3.     m-cresol     yellow-  yellow- yellow                                          purple       green    green                                            4.     neutral red  orange   orange  orange                                   5.     chlorophenol purple   purple  yellow                                          red                                                                    6.     bromocresol  blue     blue    yellow-                                         green                         green                                    7.     methyl red   yellow   red-    red                                                                   yellow                                           8.     bromophenol  purple   purple  yellow                                          red                                                                    9.     hematoxylin  red      light   light                                                                 red     yellow                                   10.    alizarin     light    light   light                                                        purple   purple  yellow                                   11.    propyl red   yellow   yellow- yellow-                                                               red     pink                                     12.    bromophenol  blue     blue    green                                           blue                                                                   ______________________________________                                    

EXAMPLE 16

To one-ml aliquots of the solutions of Example 13 is added 16 μL of 1 MTris-HCl at pH 8.0. This is equivalent to 8 mM titratable Tris base inthe final solutions. Three 25 μL aliquots of the resulting solutions arepipefitted onto a glass plate and allowed to air dry. The drying iscomplete in one hour. The dried films are subjected to 0, 15, or 60minutes of solar illumination on a clear February day in San Diego,Calif. and the colors noted. The observed color changes are listed inTable 13.

                  TABLE 13                                                        ______________________________________                                                      OBSERVED COLOR                                                  INDICATOR DYE   Initial  15 min.   60 min.                                    WITH 8 mM Tris-HCI                                                                            Color    Sunlight  Sunlight                                   ______________________________________                                        1.     bromothymol  blue-    blue-   yellow                                          blue         green    green                                            2.     ethyl red    yellow   yellow  red                                      3.     m-cresol     yellow-  yellow- yellow                                          purple       green    green                                            4.     neutral red  orange   orange  orange                                   5.     chlorophenol purple   purple  yellow                                          red                                                                    6.     bromocresol  blue     blue    yellow-                                         green                         green                                    7.     methyl red   yellow   yellow  red                                      8.     bromophenol  purple   purple  yellow                                          red                                                                    9.     hematoxylin  red      red     light                                                                         yellow                                   10.    alizarin     light    light   light                                                        purple   purple  yellow                                   11.    propyl red   yellow   yellow  yellow-                                                                       pink                                     12.    bromophenol  blue     blue    green                                           blue                                                                   ______________________________________                                    

Examples 17 and 18, relate to the advantageous use of buffering agents,such as Tris-HCl, or deoxycholate, to lengthen the time in which a colorchange is observed and to detect an increased amount of ultravioletradiation.

EXAMPLE 17

To one-ml aliquots of the solutions described in Example 13, is added 6μL of 1 M Tris-HCl at pH 8.0. This is equivalent to 3 mM titratable Trisbase in the final solution. Three 25 μL aliquots of any one of theresulting solutions are pipefitted onto a glass plate and allowed to airdry. The drying is complete in one hour. The dried films are subjectedto 0, 15, or 60 minutes of solar illumination on a clear February day inSan Diego, Calif. and the colors noted. The observed color changes arelisted in Table 14.

                  TABLE 14                                                        ______________________________________                                                      OBSERVED COLOR                                                  INDICATOR DYE   Initial  15 min.   60 min.                                    WITH 3 mM Tris-HCl                                                                            Color    Sunlight  Sunlight                                   ______________________________________                                        1.     bromothymol  blue-    green   green                                           blue         green                                                     2.     ethyl red    yellow   yellow- red-                                                                  red     yellow                                   3.     m-cresol     yellow-  yellow- yellow                                          purple       green    green                                            4.     neutral red  orange   orange  orange                                   5.     chlorophenol purple   purple  purple                                          red                                                                    6.     bromocresol  blue     blue    light                                           green                         green-                                                                        blue                                     7.     methyl red   yellow   red-    red-                                                                  yellow  yellow                                   8.     bromophenol  purple   purple  purple                                          red                                                                    9.     hematoxylin  red      light   light                                                                 red     brown                                    10.    alizarin     light    light   v. light                                                     purple   purple  purple                                   11.    propyl red   yellow   yellow- yellow-                                                               red     red                                      12.    bromophenol  blue     blue    blue                                            blue                                                                   ______________________________________                                    

EXAMPLE 18

To one-ml aliquots of the solutions of Example 13 is added 16 μL of 1 mMTris-HCl at pH 8.0. This is equivalent to 8 mM titratable Tris base inthe final solution. Three 25 μL aliquots of any one of the resultingsolutions are pipefitted onto a glass plate and allowed to air dry. Thedrying is complete in one hour. The dried films are subjected to 0, 15,or 60 minutes of solar illumination on a clear February day in SanDiego, Calif. and the colors noted. The observed color changes arelisted in Table 15.

                  TABLE 15                                                        ______________________________________                                                      OBSERVED COLOR                                                  INDICATOR DYE   Initial  15 min.   60 min.                                    WITH 8 mM Tris-HCl                                                                            Color    Sunlight  Sunlight                                   ______________________________________                                        1.     bromothymol  blue-    blue-   blue-                                           blue         green    green   green                                    2.     ethyl red    yellow   yellow  yellow                                   3.     m-cresol     yellow-  yellow- yellow-                                         purple       green    orange  green                                    4.     neutral red  orange   orange  orange                                   5.     chlorophenol purple   purple  purple                                          red                                                                    6.     bromocresol  blue     blue    blue                                            green                                                                  7.     methyl red   yellow   yellow  yellow                                   8.     bromophenol  purple   purple  purple                                          red                                                                    9.     hematoxylin  red      red     light                                                                         red                                      10.    alizarin     light    light   light                                                        purple   purple  purple                                   11.    propyl red   yellow   yellow  yellow-                                                                       orange                                   12.    bromophenol  blue     blue    blue                                            blue                                                                   ______________________________________                                    

The following example, Example 19, demonstrates the retardant effect ofsodium deoxycholate upon the acidification of the dye and alsodemonstrates the use of a liquid medium contained in a Saran™ plasticwrap support.

EXAMPLE 19

A solution of 2-ethoxy-ethoxy-ethanol is made 1.0 M inortho-nitrobenzaldehyde and 10 mM in bromothymol blue. The pH of thesolution is adjusted to pH 9.2 by addition of 400 μL 1 M NaOH to a 22 mlvolume of solution. At this pH, bromothymol blue has a deep blue-greencolor. A second solution is similarly prepared except that in additionit is made 100 mM in sodium deoxycholate. Mixture of these two solutionsin proportions of 9:1 and 4:1 provides solutions respectively 10 mM and20 mM in deoxyoholate. These solutions, when exposed to direct sunlightundergo a color change to yellow in the following times: 0 deoxycholate,5 minutes; 10 mM deoxycholate, ca. 20 minutes; and 20 mM deoxycholate,ca. 30 minutes.

Similar solutions, 25, 50, 75 and 100 mM in deoxycholate were sealedinto adjacent segments between two sheets of heat sealable plastic usinga hot wire.

These sections changed color from dark blue-green to yellow in 22, 45,80 and 120 minutes, respectively. In a similar experiment employingchlorophenol red, the color change from violet red to yellow occurred in15, 30, 38 and 50 minutes at the progressively higher concentrations ofdeoxycholate.

The use of a pH adjuster for the purpose of extending the temporalelements of the color transitions possible for a particular dye isillustrated in the following example, Example 20. The addition of the pHadjuster differs from the addition of a buffer. While both a buffer anda strong base extend the time required for a color transition to occur,only a strong base will always alter the initial pH and correspondinginitial color.

EXAMPLE 20

Ten ml of 7.2% polyvinyl alcohol was made 1 mM in bromothymol blue and50 mM in a bisulfite adduct of ortho-nitrobenzaldehyde. Addition of 100μL of 1.0 M NaOH results in a color change from the yellow acid form ofthe dye to the blue basic form. An equivalent amount of titratablephosphate added to the original solution as a potassium phosphate bufferat pH 6, allows for the formulation of a film which will turn yellowafter the same amount of illumination as the film to which sodiumhydroxide was added, but which will be initially green rather thaninitially blue.

Examples 21, and 22 relate to systems which can be used for quantifyingexposure to ultraviolet radiation in a variety of settings includingpersons or objects exposed to natural or artificial sources.

EXAMPLE 21

A buffer, such as sodium deoxycholate, is applied in the form of aconcentration gradient from 0 to 20 mM of across the long axis of a thinstrip plastic backing coated with diethylaminoethyl cellulose. Severalcoats of a solution 8% in polyvinyl alcohol, 50 mM inortho-nitrobenzaldehyde bisulfite adduct, 1 mM in bromothymol blue, and10 mM in NaOH is applied with an aspirator type sprayer to the strip.Being more basic than the dye, the deoxycholate functions as a bufferand proportionally attenuates the appearance of a color changeprogressively from one end of the strip to the other. Graduationswritten across the top of the strip indicate ultraviolet exposure andare read by their alignment with the interface between the basic andacidic colors of the dye.

Alternatively, one or more dyes, or the buffer, are deposited in variouspatterns to provide for more complex and/or visually appealing responsesto light. By use of a computer controlled printing process fordeposition of buffer and/or dyes, considerable complexity can begenerated including graphic and alphanumeric patterns.

EXAMPLE 22

In this example embodiments are described as useful for measuring theamount of incident ultraviolet light over an extended period of time bythe juxtaposition of variously reactive formulations.

Each formulation may contain the same dye; however, for visual interestseveral dyes may be used. Each formulation has a proportionally greateramount of buffer, and so is more or less reactive. The formulations canbe cut into squares for example or any other suitable shape. Variouspolyvinyl alcohol formulations are prepared, as previously described inExamples 17 and 18, each containing for example a two-fold increase inthe amount of buffer present. That is, the first formulation contains Xamount; the second contains 2X; the third, 4X; the fourth, 8X; and up to512X if, for example, ten formulations are chosen. One or more dyes maybe used and appropriate color standards are provided for each dyeemployed. Numbers beside each progressively more heavily buffered squareindicate how much ultraviolet radiation is required to cause a change ofcolor and the total exposure is readily discerned by comparing the testsquares to the standard squares.

Three rows of squares, cut from different polyvinyl alcoholformulations, are applied to a plastic strip. One of the outer rowsrepresents the standard color for each dye in its initial/basic colorstate and the other outer row represents the standard color for each dyein its final/acidic stage. The middle row is the test row which changescolor to an extent dependent upon the amount of incident ultravioletlight exposure. As the amount of exposure increases, the number ofsquares which have changed color from the initial to final color willincrease. The total number of squares which have changed color is adirect indication of the total amount of exposure to ultraviolet light.

The devices described in Examples 21 and 22, may be supplied in lightsecure packaging from which they are removed and applied to a surface,such as skin or clothing, by means of an adhesive backing which isexposed by removing a protective film, not unlike a self-adhesivebandage. Alternatively, the devices described above may be appliedthrough use of other means such as badges or bracelets having slotswhich receive and protect the devices.

Alternatively the devices may be coated on the sun-ward surface with amaterial, such as collagen, which has an affinity, quantitativelysimilar to that of human skin, for one or more brands of commercialsunscreen ointment. Sunscreen is applied to the device so that thedevice and can thereby be used to monitor the effectiveness of theultraviolet blocking action of residual sunscreen even as it is beingwashed or worn off over extended periods.

The following example, Example 23, illustrates a procedure for makingphototranschromic inks which can be effectively used on a variety ofsurfaces such as cloths, papers, cardboards, and other receptivesurfaces, and which can be adapted for a variety of commercial andindustrial applications where it is advantageous to createphototranschromic effects.

EXAMPLE 23

An ink was compounded in the following manner. An aqueous solutioncontaining 20% diethylene glycol and 0.8% polyvinyl alcohol was made 200mM in the bisulfite adduct of orthonitrobenzaldehyde, 10 mM inbromophenol blue and 20 mM in NaOH. When applied to paper with a brush,the ink adhered smoothly and dried rapidly. The color was deep bluewhich changed through green to yellow under direct solar illuminationfor about half an hour.

Alternatively, multiple inks or paints can be made to all initiallyappear the same color, but which upon subsequent exposure to ultravioletlight develop into multiple colors, These inks may be prepared as inExample 23, using any single dye or appropriate combination of dyes asin Example 24.

The following example illustrates the use of a pH sensitive dye incombination with a relatively pH insensitive dye to modify the initialand final color states obtainable.

EXAMPLE 24

Xylene cyanol, a relatively pH insensitive blue dye is combined withethyl orange, a pH sensitive dye, yellow in its basic state and red inits acidic state. An 8.5% solution of polyvinyl alcohol is made 50 mM inthe bisulfite adduct of ortho-nitrobenzaldehyde and 10 mM in NaOH. Dyesare added in the concentrations listed below and the solutions areapplied to glass plates and allowed to evaporate into thin films. Thefilms are exposed to direct sunlight for 90 minutes and the initial andfinal colors are as listed in Table 16.

                  TABLE 16                                                        ______________________________________                                        Ethyl orange                                                                  Initial/Final                                                                            Xylene cyanol Colors                                               ______________________________________                                        1.0 mM     1.0 mM        bright med. green/                                                            smokey purple                                        1.0 mM     0.5 mM        bright med. green/                                                            greenish purple                                      1.0 mM     0.2 mM        light blue-green/                                                             reddish green                                        0.2 mM     0.2 mM        yellow-green/                                                                 light burgundy                                       ______________________________________                                    

Plastics can be formed or molded into various shapes, such as toys,which upon subsequent exposure to ultraviolet light develop multiplecolors. The following example describes a method for constructingthree-dimensional silicone objects the color of which can be transformedby ultraviolet light.

EXAMPLE 25

To 100 ml of Petrarch SS curable silicone dispersion (Petrarch Systems,Inc., Bristol, Pa.) was added 750 mg orthonitrobenzaldehyde, and asolution consisting of 1 ml of 100 mM chlorophenol red in ethanol towhich had been added 1 ml of 1.0 M NaOH. The thick dispersion was a deepreddish-purple and was placed in a 500 ml beaker for several days afterwhich it was dry, firm, and pliable and could be easily cut with a sharpblade. Several geometrical shapes were cut from this material and whenilluminated with ultraviolet radiation for an hour, the illuminatedsurface changed color from purple to yellow. However, the siliconesystems discolored over time and became inactive to the action of UVradiation.

Example 26 relates to phototranschromic materials which can be used inconjunction with photographic negatives or transparencies to producemodified images wherein contours and shapes in the photographic imageare rendered in the phototranschromic materials into colors which areinherent in the phototranschromic material.

EXAMPLE 26

Images can be prepared in which negatives or transparencies are placedon a sheet of the ultraviolet reactive materials and exposed toultraviolet light.

The ultraviolet light is selectively transmitted depending upon theimage present in the negative or transparency so that color changes willonly occur where the ultraviolet light is transmitted.

A black and white 35 mm negative developed from an exposure of Kodak™Tri-X film is held in place between a section of the film described inExample 14 and a source of ultraviolet illumination for thirty minutes.A clearly defined image is produced on the phototranschromic filmwherein the darker areas of the Kodak™ negative are rendered in reddishbrowns, the lighter parts of the Kodak™ negative are rendered in yellowand the grey tones are rendered in intermediate shades.

The following example, Example 27, demonstrates the use ofphototranschromic films to create images of various three-dimensionaltemplates juxtaposed between the film and a source of ultravioletillumination.

EXAMPLE 27

One hundred ml of a solution of 8% polyvinyl alcohol, 50 mM in thebisulfite adduct of ortho-nitro-benzaldehyde and 10 mM in NaOH is pouredonto a glass plate and allowed to evaporate for 16 hours. The dried filmcovers 780 square centimeters and is dark red- brown. A section of thefilm is placed on the flat surface in direct sunlight for 30 minuteswith a coiled wire on its sunward side. The shadow of the coil leaves arelatively unchanged red-brown image on a background which turns yellow.The image is sharp and stable after the film is removed from thesunlight.

The use of a crystalline bisulfite adduct of ortho- nitrobenzaldehyde,rather than the adduct prepared in situ as described in Example 12,requires an extra preparative step but confers several advantages.First, the crystallized material represents a relatively purified sourceof ortho-nitrobenzaldehyde as compared to the commercially availablealdehyde. Second, the ratio of aldehyde to bisulfite is fixed by thestoichiometry of the chemical interaction rather than a weighingoperation, and is therefore more reliably reproducible. Third, no excessof bisulfite (which acts as a buffer in certain pH ranges) is requiredto produce a clear solution, as is necessary in the case of the in situpreparation of the adduct as described in Example 12. Example 28 relatesto the preparation and use of a crystalline ortho-nitrobenzaldehydebisulfite adduct which can be used in all of the previous examples toreplace in situ generated orthonitrobenzaldehyde bisulfite adduct.

EXAMPLE 28 A. Preparation of Crystalline Bisulfite Adduct

To prepare the ortho-nitrobenzaldehyde bisulfite adduct, approximatelyequal molar amounts of sodium bisulfite and ortho-nitrobenzaldehyde areused. For example, one hundred grams of sodium bisulfite are dissolvedin 200 ml of water, at room temperature. A mixture of 132 grams ofortho-nitrobenzaldehyde in 100 ml ethanol is dissolved by heating and isimmediately added with stirring to the sodium bisulfite solution. Thesolution of ortho-nitrobenzaldehyde and bisulfite is protected fromlight and left overnight at room temperature are filtered and rinsedwith ethanol prior to drying at room temperature.

B. Use of Crystalline Bisulfite Adduct

To 1000 ml of an 8% polyvinyl alcohol solution is added 6.37 g ofortho-nitrobenzaldehyde sodium bisulfite crystals (25 mM) (as preparedin part A), 258 mg of methyl green (Eastman Kodak, Rochester, N.Y.)dissolved in 10 ml of H₂ O (0.5 mM) and 20 ml of 1.0 M NaOH (2 mM). Thesolution is mixed and poured onto a clean glass plate and allowed to dryat room temperature, at approximately 60% relative humidity, for 24-48hours or until dry to the touch. Upon exposure to UV light, the filmundergoes a color change from light blue to a deep forest green.

The following example, Example 29 relates to the preparation ofmultilaminate films. There are multiple advantages to using anarrangement, such as a laminate, of two separately produced layers offilm rather than combining several dyes in the same active layer. One isthat the multiple dyes can be initially set to a different pH. Second,buffers can be added independently to either layer to prolong or shortenthe color transition period. Third, the shielding of lower layer(s) fromultraviolet radiation by upper layer(s) causes a differential rate ofactivation to occur in the different lower layers.

EXAMPLE 29

A solution of 8% polyvinyl alcohol, 25 mM in the crystalline bisulfiteadduct of orthonitrobenzaldehyde and 0.5 mM in bromophenol blue isbrought to pH 4.4 with 1 M NaOH and poured (cast) onto a clean glassplate. A second solution of 8% polyvinyl alcohol, 25 mM in the bisulfiteadduct of ortho-nitrobenzaldehyde and 0.15 mM in methyl orange isbrought to pH 4.6 with 1 M NaOH and poured (cast) onto a second cleanglass plate. Both solutions are allowed to evaporate at room temperatureand at approximately 60% relative humidity for 24-48 hours until dry tothe touch. The two types of film thus produced can be laminated togetherusing, for example, a clear polyethylene film coated on both sides withacrylic adhesive. The lamination can also be accomplished in other ways;for instance a thin layer of an acetone solution of polyvinylacetate mayserve to join two polyvinyl alcohol films together.

Next, the methyl orange side, for example, of the compound film thusproduced is attached to a white vinyl backing coated with a similaradhesive. This assembly, when subjected to varying amounts of UVradiation, e.g,, from 1.5 to 10 Joules/cm², changes from an initialcolor of medium blue, to light green, to clear yellow, to light orange,to orange-red. Similar laminations or juxtapositions, using two or morelayers of other films, prepared as described in the previous examples,have been produced with similarly effective results.

The choice of film thickness depends upon a balancing of at least twofactors including: i) the advantageous shorter drying times associatedwith using thinner films and ii) the concomitant decreased opticaldensity of thinner films and resultant decreased color intensity. Verythin films, for example thinner than 10 microns, are easier tomanufacture in a continuous process due to their shorter drying times.High dye concentrations, to compensate for the decreased opticaldensity, of up to 10 mM, can be used. In Example 30, mixtures of dyecomponents are shown to lead to films which produce ranges of colorchanges which are more diverse and useful than those fabricated with asingle dye. Often the effect of including multiple dyes in the film isto yield more color changes in a serial manner. Also, the use ofmultiple dyes makes available more aesthetically appealing colorcombinations than is available through single dye formulation. Theultimate colors and intermediate color changes are not readily predictedfrom the observation of single dye films.

EXAMPLE 30

To 10 ml. of an aqueous solution containing 8% (wt/vol.) polyvinylalcohol (Vivol 1 25, Air Products), 25 mM ortho nitro benzaldehyde and28 mM sodium bisulfite was added 0.01 millimolar of two dyes as listedin Table 17. Initial pH were adjusted to the high limit of the mutualindicator system with the addition of 1 Molar sodium hydroxidesolutions. The mixtures were case onto glass plates and allowed to airdry overnight. Each combination was exposed to natural sunlight andevaluated for color change and appearance of in Table 17.

                  TABLE 17                                                        ______________________________________                                        DYE           INITIAL   FINAL                                                 MIXTURE       COLOR     COLOR    COMMENTS                                     ______________________________________                                        1.  Alizarin Yellow                                                                             pink-     pink-  subtle                                         R Alizarin    violet    yellow                                            2.  Alizarin Yellow                                                                             blue-     army-  indistinct                                     R Lacroid     green     green                                             3.  Alizarin Yellow                                                                             light-    reddish-                                                                             indistinct                                     R Resazurin   purple    purple                                            4.  Alizarin Yellow                                                                             yellow    yellow no change                                      R Indigo                                                                      Carmine                                                                   5.  Alizarin Yellow                                                                             yellow    yellow no change                                      R 4 Amino                                                                     Azobenzene                                                                6.  Alizarin      blue      black                                                 Lacroid                                                                   7.  Alizarin      violet    red-   crystal-                                       Resazurin               violet lites                                                                         found in                                                                      film                                       8.  Lacroid       blue      dark-                                                 Resazurin               purple                                            9.  Lacroid       blue      ugly-  poor                                           Carminic Acid           green  colors                                     10. Indigo Carmen light     tan                                                   Carminic Acid blue                                                        11. Bromophenol Blue                                                                            blue      blue/  poor                                           Chlorophenol            green  change                                         Red                                                                       12. Bromophenol Blue                                                                            light     dark   very                                           Ethyl Violet  blue      blue   distinct                                   13. Bromophenol Blue                                                                            blue      light                                                 Ethyl Red               green                                             14. Chlorophenol Red                                                                            light     orange wine color                                     Neutral Red   violet                                                      15. Chlorophenol Red                                                                            grey-     orange                                                Ethyl Red     purple                                                      16. Chlorophenol Red                                                                            purple    violet indistinct                                     Methyl Red    green                                                       17. Orthocresol Purple                                                                          blue      orange very                                           Bromophenol Blue               distinct                                                                      changes                                    18. Aniline Blue  reddish   green  distinct                                       Phenol Red    purple           changes                                    19. Nile blue     light     red                                                   Methyl Red    green                                                       ______________________________________                                    

EXAMPLE 31

An aqueous solution 4% in polyvinyl alcohol, 25-50 mM in the bisulfiteadduct of orthonitrobenzaldehyde, and from 0.1 to 10 mM in aniline blueand from 0.1 to 10 mM in phenol red, preferably in a ratio of anilineblue to phenol red of 2 to 5, and 10 mM in NaOH, is poured onto a glassplate. The solution is spread into a layer, ca. 100 microns thick, andis allowed to dry into a layer ca. 10 microns thick. The film thusproduced is a reddish purple initially and upon ultraviolet irradiationchanges through orange to yellow and finally to green. Prior to removalfrom the glass plate, the thin film is attached to a white vinyladhesive backing to protect it from mechanical deformation uponseparation and during later handling. A thin layer of Mylar™, or someother moisture barrier, is attached via an acrylic adhesive transfertape to the unbacked side of the film to further protect it.

EXAMPLE 32

It has been observed that, for certain dyes, a discoloration of thepost-ultraviolet irradiation color sometimes occurs. To prevent thispost-irradiation discoloration, it has been found that a suitableantioxidant, such as hexamethylenetetramine (0.02 to 0.05% w/v) can beadded to the film formulations prior to casting.

Ultraviolet light reactive films of the invention, also referred to as"polychromatic" films, can be made which pass through several differentand distinct colors in response to increasing amounts of ultravioletlight. The polychromatic films display intermediate colors which are notsimple mixtures of the initial and final colors. Example 31 relates tosuch a film which is made from the mixture of aniline blue and phenolred and which changes from purple to red to yellow to green. Theintermediate colors observed, e.g., red and yellow, are not simplemixtures of the initial (purple) and final (green) color states.

Various compounds which are transparent in the visible range but whichstrongly absorb in the ultraviolet range can be used in combination withthe films of the invention to modify the films' responsiveness toultraviolet radiation. If a layer of a transparent plastic, on which isdeposited various amounts of such a compound, such as Cyasorb UV24™, orCyasorb UV9™, etc, (American Cyanamid, Bridgewater, New Jersey) islaminated over a layer of the films of the invention, the color changeresponse to ultraviolet light will be altered in proportion to theamount of Cyasorb™ which effectively "masks" any given area.

If desired, complex patterns of Cyasorb UV24™ can be applied to atransparent plastic layer by incorporating the Cyasorb™ directly into aprinting ink and applying the printing ink to the plastic with, forexample, a printing press. Several different inks can be prepared,containing different concentrations of Cyasorb™ and, when thesedifferent concentrations are used in a multi-color printing process, asthough they were different colors of ink, the pattern, or picture,applied to the transparent plastic film can be "transferred" to anunderlying layer of polychromatic films, such as those films describedin Example 14 or in Example 31, by exposing the entire laminate assemblyto a specified amount of ultraviolet light.

Alternatively, the printing of patterns with ultraviolet absorbing inksmay be done directly onto the polychromatic films. Ideally, in thislatter process, the inks used should be both chemically and physicallycompatible with the polychromatic films, i.e, the inks must not exhibitacid-base reactions in the working pH range of the films of theinvention or chemically interfere in any other way.

Various interesting versions of an ultraviolet dosimeter are possibleutilizing the two modifications described above. For example, variouspatterns, letters, numbers, and pictures can be directly and readilyincorporated into a strip without any manufacturing difficulty. Examplesof both modifications are described below in Examples 32 and 34.

EXAMPLE 33

Polyvinylalcohol (PVA) films were cast from solutions containing 0.2 mManiline blue, 0.5 mM phenol red, and 25 mM ortho-nitrobenzaldehydebisulfite adduct, which solutions had been titrated to pH 9.0 by theaddition of 1 M sodium hydroxide. Ultraviolet absorbing inks were madeby dissolving Cyasorb UV24.sup.™ into a transparent ink (Nazdar 70-170,Naz-dar Company, Chicago, Ill.). Using 390 mesh calendared screens andthese inks, a rectangular array pattern was printed onto thepolychromatic films. Three inks with concentrations of CyasorbUV24.sup.™ of 4%, 8%, and 16%, respectively, were used in conjunctionwith patterns in three screens, so as to deliver combinations of thethree inks resulting in eight separate rectangles ranging from 0% in theupper left hand corner to 40% in the lower right hand corner. The filmso obtained was dried and was initially a uniform shade of purple. Whenplaced in bright sunlight for approximately 40 minutes, the "invisible"latent pattern became "visible" as a pattern of variously coloredrectangles. The upper left hand rectangle was dark green (0%) and thelower right hand rectangle (40%) was still the original color of thefilm, e.g., purple. The other rectangles were red, yellow, and lightgreen, in a regular pattern as shown in Table 18, below.

                  TABLE 18                                                        ______________________________________                                               0%          4%                                                                Dark        Green                                                             Green                                                                         8%          12%                                                               Light       Green-                                                            Green       Yellow                                                            16%         20%                                                               Yellow      Yellow-Red                                                        24%         40%                                                               Red         Purple                                                     ______________________________________                                    

EXAMPLE 34

A pattern of ultraviolet inks was printed onto a 92 gage Melinex 401clear polyester film obtained from ICI Americas, Inc., Wilmington, Del.This polyester film was then laminated to several different previouslyprepared films of the invention prepared according to Example 33. Whenthe laminated layers were exposed to ultraviolet light, the initially"invisible" pattern printed onto the polyester became "visible" in theform of an array of colored rectangles as described previously inExample 33.

In addition, by overlaying a piece of the polychromatic films with aphotographic negative, such as a medical x-ray plate, similar effectscan be produced. Significantly, an enhancement of the visuallyperceivable contrast and detail is obtained by "converting" theblack/white/grey image of the x-ray into a color image in which thevarious shades of grey are "converted" and then represented as distinctcolors.

EXAMPLE 35

An autoradiogram of a DNA sequencing gel is a pattern in black, whiteand various shades of grey representative of the positions of bandscontaining radioactive DNA in an analytical polyacrylamide gel. Whensuch an autoradiogram was placed between an ultraviolet light source andfilm, as the one described in Example 33, a replica of the photographicpattern was created in which the black spots were purple, the clearbackground was green and the intermediate shades of grey ranged from redto yellow. This pattern of colors, and specifically the substitution ofyellow or red for grey tones, where yellow or red are not intermediatecolors in an additive sense between purple and green, enhances thedetail and the contrast apparent to the human observer.

EXAMPLE 36

Two films prepared as detailed in Example 30 and corresponding toExamples 17 and 18 in Table 17 were cut into 1/4 "by 1" strips placedinto small vials and subjected to accelerated aging at 60 degrees Cuntil visual indication of a change from the original color wasobserved. Example 17 in Table 17 corresponds to a low pH formulation (pH<7) and exhibited excellent thermal stability being unchanged after 3months at 60 degrees C. Example 18 in Table 17 corresponds to a high pHformulation (pH >7) and exhibited very poor thermal stability havingchanged in color after 24 hours at 60 degrees C.

The foregoing illustrative examples relate to systems responsive to andfor visualization of ultraviolet radiation. While the present inventionhas been described in terms of specific methods and compositions, it isunderstood that variations and modification will occur to those skilledin the art upon consideration of the present invention.

For example, it is envisioned that various compounds capable ofgenerating a proton or hydrogen ion upon exposure of ultraviolet lightwill be effective according to the present invention. Although thepreferred compounds are ortho-nitrobenzaldehyde; 2,4-nitrobenzaldehyde;ortho-nitrocinnamaldehyde; and 2,6-dinitrobenzaldehyde; it is notintended to preclude others such as any aromatic ortho-nitro formylcompound or any other effective compound from being included in thescope of the present invention.

Inasmuch as other aromatic ortho-nitro formyl compounds, are classifiedwith orthonitrobenzaldehyde as regards their ability to generate protonupon exposure to ultraviolet radiation, and are, therefore, likely to besimilarly effective, it is intended that these substances be includedwithin the scope of the present invention as well.

The foregoing examples demonstrate the utility of dyes such as Alizarin,Alizarin yellow R, Alizarin red s, Benzopurpurin 4B,4,4'-bis(4-amino-1-naphthyl-azo)-2,2'-stilbene-disulfonic acid,Brasiline, Bromocresol green, Bromocresol purple, Bromophenol blue,Bromophenol red, Bromothymol blue, Bromoxylenol blue, Carminic acid,Chlorophenol red, Congo red, m-Cresol purple, Cresol red, Curcumin,3-(4-Dimethylamino-1-naphthyl-azo)-4-methoxybenzene-sulfonic acid,Direct red, Eriochrome black T, Erythrosin B,4-(4-Ethoxy-phenylazo)-3-phenylene-diamine hydrochloride, Ethyl orange,Ethyl red, Ethyl violet, Rematoxylin, Lacmoid, Litmus, Metanil yellow,Methyl green, Methyl red, Naphtholphthalein, Neutral red, Nile blue A,Orange I, 4-(Phenylazo)diphenylamine, Phenol red, Propyl red, Resazurin,Thiazole yellow G, Thymol blue, Tropaeoline 00, and p-Xylenol blue. Itis envisioned that other dyes will prove to be equally effective. Suchother dyes include, for example those listed in Kodak LaboratoryChemicals, catalogue No. 52 (July 1, 1985) pages 615-620 or othersimilar sources. Accordingly, it is intended that these other dyes beincluded within the scope of the invention.

Additionally, it is intended that other media than polyvinyl alcoholhaving similar hydrophilic characteristics will prove to be effective inthe formulation of films, fibers, inks, paints, and the like; providedthey are coated with a material barrier which is relatively impermeableto molecular oxygen, impregnated with the antioxidants, or a combinationor these two. It is intended that other media be included in the scopeof the invention.

In addition, although bisulfite is described as the compound used toincrease the solubility of the photoacid progenitor, other compounds,such as bisulfite derivatives, surfactants or other compounds capable ofincreasing solubility, are to be inclined within the scope of theinvention.

It is anticipated that buffering agents other than Tris-HCl,deoxycholate, or phosphates will prove to be equally effective infunctioning as buffers. Such other buffering agents include any with apK greater than the particular dye employed, such as, amines,piperidine, purine, proline, and the like. Therefore, it is intendedthat these are included in the scope of the present invention.

It is anticipated that pH adjusters other than sodium hydroxide, willprove to be equally effective in functioning as pH adjusters such as anystrong base including potassium hydroxide, calcium hydroxide and thelike. Similarly, it is anticipated that anti-oxidants other thanhexamethylenetetramine will prove to be equally effective. Therefore, itis intended that these are included in the scope of the presentinvention.

It will be understood that a variety of techniques may alternatively beapplied to provide various materials with the above properties which canbe cast into films, extruded into fibers, molded into shapes, formulatedas inks, paints, and the like. In addition, it will be understood thatvarious modifications in format can be employed to measure the amount ofincident ultraviolet light over a specified period of time.

It is contemplated that other formats and physical arrangements andjuxtapositions of the materials will be manufactured by those skilled inthe art and employed according to the present invention. These alternateformats, arrangements, and juxtapositions are also intended to comewithin the scope of the invention as claimed.

Numerous modifications and variations in the invention as described inthe above illustrative examples are expected to occur to those skilledin the art and consequently only such limitations as appear in theappended claims should be placed thereon.

Accordingly, it is intended in the appended claims to cover all suchequivalent variations which come within the scope of the invention asclaimed.

What is claimed is:
 1. An ultraviolet dosimeter that indicatescumulative exposure to ultraviolet radiation that comprises:a) a filmthat is substantially impermeable to oxygen and changes from one colorto a different color in response to exposure to ultraviolet radiationthat comprises a mixture of:i) from about 50 to about 99 weight percentpolyvinyl alcohol; ii) from about 0.5 to about 50 weight percent water;iii) from about 0.01 to 5 weight percent of at least one acid-sensitivedye that is substantially insensitive to changes in temperature; iv)from about 0.05 to about 5 weight percent of a surfactant; and v) fromabout 1 to about 40 weight percent of a photoacid progenitor comprisinga bisulfite adduct of an ortho nitro-substituted aromatic aldehyde thatis converted into a photoacid on exposure to ultraviolet light; b) anultraviolet radiation transparent moisture barrier adhered to andsurrounding said film; c) a color standard chart that is affixed to saiddosimeter and is in close visual proximity to said film; and d) means toaffix the dosimeter to user.